1. Field of the Invention
The present invention is related to a process for the removal of sulfur oxides from flue gas.
2. State of the Art
An economical method of removing sulfur dioxide, SO.sub.2, from flue gases consists of injecting calcium hydroxide crystals, called hydrate, into flue gases at stack temperatures of about 300.degree. F., and then injecting a water spray. The water droplets contact the SO.sub.2, some of which dissolves forming H.sub.2 SO.sub.3. The H.sub.2 SO.sub.3 then contacts hydrate particles and reacts, forming CaSO.sub.3 and water. A mixture of the CaSO.sub.3 formed, unreacted hydrate and flyash is recovered in a downstream particulate-removal device, such as an electrostatic precipitator, baghouse or the like, and desulfurized flue gases are recovered or sent to a stack. A major drawback to this process is that large excess amounts of hydrate are used because much of the hydrate escapes unreacted when the H.sub.2 SO.sub.3 evaporates before it contacts the hydrate particles, and reverts back to SO.sub.2 and water vapor.
The object of the present invention is to increase the efficiency of the conversion of hydrate to CaSO.sub.3 in flue gas desulfurization. This has the dual benefits of (a) removing more SO.sub.2 per pound of hydrate injected, and (b) requiring less hydrate to be injected, thus reducing costs. The efficiency will be increased by cooling the hydrate before, or during, injections.